You should swallow a toad every morning, when going out into high society, so as to encounter nothing more disgusting during the day.
 
[Faudrait avaler un crapaud tous les matins, pour ne trouver plus rien de dégoûtant le reste de la journée, quand on devait la passer dans le monde.]

Nicolas Chamfort (1741-1794) French writer, epigrammist (b. Nicolas-Sébastien Roch)

Products of Perfected Civilization [Produits de la Civilisation Perfectionnée], Part 2 “Characters and Anecdotes [Caractères et Anecdotes],” ch. 5 (1795) [tr. Dusinberre (1992)]
    (Source)

Though usually attributed directly to Chamfort, he credits the phrase to a M. de Lassay.

Fragment 863. (Source (French)). Alternate translations:

It would be necessary to swallow a toad every morning, in order not to find anything disgusting the rest of the day, when one has to spend it in the world.
[tr. Matthews (1877)]

One must swallow a toad every morning, when one has to go out in the world, so as not to find anything more disgusting during the day.
[tr. Merwin (1969)]

Swallow a toad in the morning and you will encounter nothing more disgusting the rest of the day.
[Source]